Various automotive vehicles have recently begun including vehicle dynamic control systems. Such vehicle dynamic control systems include yaw stability control systems, roll stability control systems, integrated vehicle dynamic control systems, etc. The ongoing goal of vehicle control systems is to achieve a coordinated system level vehicle performance for ride, handling, safety and fuel economy.
With current advances in mechatronics, vehicle controls have increased opportunities for achieving control performances using the information and the control strategies which were previously reserved for spacecraft and aircraft. For example, gyro sensors, previously only used in aircraft, have now been incorporated in various vehicle controls, and the anti-lock brake systems once invented for airplanes are now standard automotive control systems. Current sensor technology generates ever-increasing opportunities for vehicle control. A typical vehicle control system has to sense three-dimensional dynamic vehicle motions in order to achieve high control performance and high accuracy/precision dynamics control. For example, during yaw stability and roll stability controls, the control task involves three-dimensional motions along the vehicle roll, pitch, and yaw directions and along the vehicle longitudinal, lateral and vertical directions.
The axle loading (or the vertical loading) of a moving vehicle can be directly measured by force or load measuring systems (for example, as in U.S. Pat. No. 5,265,481 or U.S. Pat. No. 5,002,141). Such systems are very expensive and usually are not cost feasible for on-vehicle implementation.
The need for sensing axle/wheel loadings of a moving vehicle is desirable in various vehicle dynamics control systems. One application of such sensing is in a roll stability control application. A roll stability control system controls the rollover characteristics of a vehicle in order to maintain its position with respect to the road, i.e., to alter the vehicle roll condition such that its motion along the roll direction is prevented from achieving a predetermined limit (rollover limit) with the aid of the actuation from the available active systems such as controllable brake system, steering system, suspension system, etc. Since the available active control systems need to deliver other normal functions (for example, a brake system needs to conduct anti-lock braking, traction control, yaw stability control, etc), it is desired that the rollover control function is only conducted on-demand, i.e., when the potential vehicular rollover happens and is turned off when the vehicle is driving in normal conditions or in the conditions outside the activation criteria of roll stability control. Therefore, the identification of a rollover condition becomes a very important factor for the successful implementation of roll stability control system. A rollover happens when the vehicle loses wheel loading at one or two wheels at the same side of the vehicle and the vehicle roll angle diverges. An on-vehicle and real-time sensing of the wheel loadings can be used to detect such pre-rollover characteristics. That is, if the predicted wheel loading or loadings are significantly smaller than its nominal value, a potential rollover condition is identified.
Another application of the axle and wheel normal loading determination is to conduct brake distribution for anti-lock brake or yaw stability control systems.
A further application of the axle and wheel loading determination is wheel control in a vehicle with a controllable suspension. The interaction between the wheel and the road plays a key role for a vehicle to maximize its stability during handling maneuvers and for a vehicle to reduce road damage (especially for heavy trucks). This performance requirement has become practical nowadays with the implementation of controllable suspensions. The performance requirement is to maintain constant axle/wheel loadings. In order to achieve such performance, feedback control signals need to be constructed from the axle/wheel loadings. Hence, dynamically determining the axle/wheel loading is required.
The fourth need for dynamically determining the axle and wheel loadings of a moving vehicle is in accurately characterizing the tire forces between the tires and the road surface. Wheel loading detection together with the real time information of the driving torque delivered to a driven wheel allows the prediction of a surface mu (coefficient of friction, μ). Knowing the surface mu is desirable for various stability control applications of vehicles.
Therefore, it is desirable to obtain a real time prediction or dynamic determination of the axle/wheel loadings of a moving vehicle without using load sensors but using available sensor signals form the various dynamic control systems and some of the calculated signals from the available sensor signals.